Anaemia is associated with higher disease activity in axial spondyloarthritis but is not an independent predictor of spinal radiographic progression: data from the Swiss Clinical Quality Management Registry

OBJECTIVE: As anaemia represents a biomarker for increased radiographic damage in rheumatoid arthritis, we aimed to investigate whether it independently predicts spinal radiographic progression in axial spondyloarthritis (axSpA). METHODS: AxSpA patients with available haemoglobin levels from the prospective Swiss Clinical Quality Management Registry were included for comparison of patients with and without anaemia. Spinal radiographic progression was assessed according to the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) in patients with ankylosing spondylitis (AS) if ≥ 2 sets of spinal radiographs were available every 2 years. The relationship between anaemia and progression (defined as an increase ≥ 2 mSASSS units in 2 years) was analysed with generalized estimating equation models after adjustment for the Ankylosing Spondylitis Disease Activity Score (ASDAS) and potential confounding, as well as after multiple imputations of missing values. RESULTS: A total of 212/2522 axSpA patients presented with anaemia (9%). Anaemic patients had higher clinical disease activity, higher acute phase reactants and more severe impairments in physical function, mobility and quality of life. In the subgroup of patients with AS (N = 433), a comparable mSASSS progression was found in anaemic and non-anaemic patients (OR 0.69, 95% CI 0.25 to 1.96, p = 0.49). Age, male sex, baseline radiographic damage and ASDAS were associated with enhanced progression. The results were confirmed in complete case analyses and with progression defined as the formation of ≥ 1 syndesmophyte in 2 years. CONCLUSION: Although anaemia was associated with higher disease activity in axSpA, it did not additionally contribute to the prediction of spinal radiographic progression.